Loose stitch forming mechanism for lockstitch sewing machines

ABSTRACT

A lockstitch sewing machine with needle and bobbin thread metering and controlling mechanisms whereby selected looseness may be provided in the threads of the resulting stitched seams including the presence of precisely controlled amounts of surplus slack thread in the seam.

United States Patent [56] References Cited UNITED STATES PATENTS 4/1916Rh0des.........................

William C. Van Ness Parsippany, NJ. 53,604

Inventor [21 Appl. No.

[22] Filed July 9, 1970 [45] Patented Dec. 21,197]

[73] Assignee The Singer Company New York, N.Y.

Robert E. Smith [54] LOOSE STITCH FORMING MECHANISM FOR LOCKSTITCHSEWING MACHINES ABSTRACT: A lockstitch sewing machine with needle and 11Claims, 10 Drawing Figs. bobbin thread metering and controllingmechanisms whereby selected looseness may be provided in the threads ofthe resulting stitched seams including the presence of preciselycontrolled amounts of surplus slack thread in the seam.

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a ATT RNEY WITNESS: Mm, Wan/M7"? PATENTEU m2] I97! SHEET 2 0F 3 INVE NTOR Willjqm C. Van Ness AT ORNEY PATENTED UEEZI IHTI SHEET 3 BF 3INVENTOR wllllom C. Van Ness LOOSE STITCH FORMING MECHANISM FORLOCKSTITCI-I SEWING MACHINES BACKGROUND OF THE DISCLOSURE In aconventional lockstitch sewing machine in which the needle thread isdirected in sequence to a thread-tensioning device, a thread takeupdevice, and thence to the needle, adjustment of the thread-tensioningdevice can influence how tightly the stitches are set into the fabricbeing sewn. With such known arrangements, however, looseness with slackor surplus thread cannot be provided in the seam by regulation of thethread-tensioning device because when this slack thread condition isapproached, a condition of uncontrolled loop formation of the sewingthreads can occur with an unsightly seam being produced, and usuallythread breakage within a relatively few stitches.

The advent of recent advances in the art of fabric treatments, such aspermanent press finishes and the like, has introduced into the art ofsewing the need for means for providing stitching which includescontrolled surplus or slack thread immediately after the stitchingoperation so that after subsequent application of pressure, heat,chemicals and chemical changes, the seams will not become puckered, butwill lie perfectly flat when the treatment is finished.

The previously known use of stitch-supporting fingers for the purpose ofproviding loose lockstitches has proven cumbersome, costly andunsuccessful in providing the accuracy of control required particularlyover the entire range of loose ness that may be required of a modernhigh-speed lockstitch machine.

BRIEF SUMMARY OF THIS INVENTION The present invention provides for theformation of controlled surplus in the sewing threads of a lockstitchseam by the use of control devices effective on the sewing threads tometer the desired surplus thread into the seam while continuouslymaintaining control of the threads to prevent looping.

Metering of the needle thread is obtained with this invention by anarrangement which directs two successive lengths of the needle thread tothe action of the takeup means with a thread nipping device interposedbetween the two lengths of thread and effective to prevent retrogrademotion of the thread, i.e., to pass thread only in a direction towardthe needle. With this arrangement, surplus thread in regulated amountsmay be drawn from a supply into the thread-manipulating system of thesewing machine in a manner which is not related to the setting of thestitches and in a manner such that the forces necessary to draw in thethread do not work to tighten the stitches being formed. Nonetheless,the system of this invention applies sufficient tension and control onthe sewing threads during the entire stitch-forming cycle thatuncontrolled flow of the thread and consequent looping is obviated.

This invention also provides for metering of the bobbin thread in alockstitch-forming machine early in or at the initiation of eachsuccessive cycle of stitch formation which has been found to assistmarkedly in the formation of relaxed loose limbs of each of the needleand bobbin threads of a lockstitch seam.

Specifically, this invention provides for a device in the form of aunitary attachment which may be applied conveniently to any conventionallockstitch machine to provide operation thereofin accordance with thisinvention.

Because only minor adjustments are required to the existingthread-handling mechanism of a lockstitch machine in order toaccommodate the present invention, a machine with the present inventionapplied thereto may also be threaded in such a way as to bypass thethread-metering facilities of this invention but yet retain the featurethat the thread is directed twice to the action of the takeup member,and this to a manually selectable degree so that conventional tightlyset stitching may be performed over an unusually wide range ofmachine-operating conditions.

With the above and additional objects and advantages in view as willhereinafter appear, this invention comprises the devices, combinations,and arrangements of parts hereinafter described and illustrated in theaccompanying drawings of a preferred embodiment in which:

FIG. 1 represents an end elevational view of a lockstitch sewing machinehaving this invention applied thereto with the faceplate removed andportions of the frame illustrated in cross section,

FIG. 2 is a side elevational view of the sewing head portion of thesewing machine of FIG. 1,

FIGS. 3, 4, 5, and 6 are perspective views of fragments of the needlethread controlling instrumentalities of the sewing machine of FIGS. 1and 2 with the parts shown in successively different positions during atypical cycle of stitch formation,

FIG. 7 is a side elevational view of a sewing head portion of a sewingmachine having a modified form of this invention applied thereto withthe needle thread shown as directed for the production of loosestitches,

FIG. 8 is a side elevational view of the sewing machine of FIG. 7 butwith the needle thread shown as directed for the production of tightstitches,

FIG. 9 is a perspective view of the loop taker of the sewing machine ofFIG. 1 showing the bobbin and needle threads at an early stage duringstitch formation and including the bobbin thread pulloff element in itseffective position for drawing off bobbin thread, and

FIG. 10 is a perspective view taken from the underside of the sewingmachine work feed dog illustrating the manner in which the bobbin threadpulloff element may be carried thereby.

FIGS. 1 and 2 illustrate this invention as applied to a sewing machinein one preferred form of construction. These figures illustrate only thehead end of the sewing machine and do not disclose, for instance, thedriving connections between the in terrelated sewing mechanisms. Suchdriving connections between the needle, loop taker and work-feedingmechanism may be of any conventional arrangement and preferably may beas disclosed in the U.S. Pat. No. 2,394,51 l of Clayton, Feb. 5, 1946 towhich reference may be had. This referenced U.S. Pat. No. 2,394,51 Ialso discloses a conventional needle thread manipulating arrangementwhich is supplanted by the novel mechanism of this invention.

Referring to FIGS. 1 and 2, 11 indicates the bed of a sewing machinefrom which raise a standard 12 supporting a bracket arm 13 whichoverhangs the bed and terminates in a hollow sewing head 14. A faceplate15 is fastened in a position covering the hollow sewing head 14 as shownin FIG. 2.

Journaled in the bracket arm 13 is a main drive shaft 20 which carriesfast thereon in the sewing head a counterbalance 21 with which isassociated two crank pins; a crank pin 22 for reciprocating a needle,and a crank pin 23 for driving a takeup mechanism.

The needle reciprocatory crank pin 22 is embraced by a drive link 24which is pivoted on a stud 25 extending laterally from a needle bar 26.The needle bar is endwise reciprocable in bearing sleeves 27 and 28 inthe sewing head and carries at the lower extremity an eye pointed threadcarrying sewing machine needle 29.

The takeup driving crank pin 23 is embraced by one extremity of a takeuplever 30 which projects out of the hollow sewing head through a slot inthe front wall and terminates exteriorly of the sewing head in athreadengaging eyelet 32. Pivoted as at 33 between the extremities ofthe takeup lever 30 is an anchor link 34 which is constrained on a pivotpin 35 fixed in the sewing machine bracket arm 13.

Also arranged in the sewing machine head is a presser bar 40 endwisemovable in a bearing sleeve 41 and carrying a work engaging presser foot42. A pressure regulating rod 43 of which an upper segment 44 isthreaded into the sewing head projects into a bore 45 in the presser barand serves to constrain a spring 46 therein for biasing the presser footdownwardly. A split block 47 secured by a clamp screw 48 to the presserbar serves three functions in the illustrated sewing machine in thatfirst it engages the sewing head 14 to prevent turning of the presserfoot; second it carries a threadengaging wire guide 49 which is securedby a screw 50 to the block 47 and which extends outwardly through a slot51 in the sewing head to exert a regulation on the needle threadmanipulation in accordance with the thickness of work fabric beneath thepresser foot, and third, it overlies a bent wire link 52 which embracesa pin 53 extending from a presser-lifting lever 54 fulcrumed along therear of the bracket arm 13 and adapted to be turned by a pull rod 55which may be connected to any conventional treadle or knee shift device(not shown).

A flexible cable 56 is clamped by a screw 57 to the pin 53 on thepresser-lifting lever 54. The flexible cable is directed through a guidetube 58 held on the sewing head by a bracket 59 and serves, as will bedescribed in detail below, to release a tension device of this inventionwhen the presser foot is raised.

As illustrated in FIG. 1, a loop taker is journaled in the bed 11 forcooperation with the needle 29 in the concatenation of threads intolockstitches. The loop taker may be of any conventional form andpreferably is operated, as described in the above referenced U.S. Pat.No. 2,394,51 l to complete two revolutions during each reciprocation ofthe needle.

A throat plate 71 which is carried on the bed 11 to support work fabricsagainst the thrust of the needle is formed with a needle aperture 72 asshown in phantom line c FIG. 9 and is also formed with slots 73 toaccommodate a work engaging feed dog 74. The feed dog is carried by afeed bar 75 which as shown in FIG. 1 is pivoted at 76 to a feed advancerock frame 77 which is secured on a feed advance rock shaft 78 journaledon the bed and serves to impart work feeding and return movements to thefeed dog. At the other extremity, the feed bar 75 is pivoted to a link79 which, in turn, is pivoted to a feed lift rock arm 80 secured to afeed lift rock shaft 81 journaled in the bed. The feed advance and feedlift rock shafts 78 and 81 may be actuated as described in the abovereferenced US. Pat. No. 2,394,5[1 to impart an oval path of motion tothe feed dog 74 moving, as viewed in FIG. I to the right and upwardlyInto engagement with a work fabric, remaining elevated while moving tothe left to feed the work, then moving downwardly out of work engagementand returning to the right while lowered beneath the throat plate.

Referring to FIG. 2 and to the above referenced US. Pat. No. 2,394,51 I,the conventional needle thread handling mechanism of the sewing machineremains largely undisturbed by the present invention and therefore, thepresent invention may be applied readily to existing lockstitch sewingmachines without requiring elaborate changes to the existing mechanisms.

Indicated at in FIG. 2 is a conventional needle thread tensioning devicewhich is arranged in the usual location on the sewing head 14 and whichincludes a check spring 91 shiftable about a central stud 92 on which isarranged a pair of tread-engaging disks 93 and an adjusting nut 94 whichordinarily serves to regulate the pressure of a beehive spring on thestud for biasing the disk 93 against each other. When the presentinvention is applied to the sewing machine, the conventionalthread-tensioning device 90 is used only for the effect of the checkspring 91, and therefore, the beehive spring may be removed as shown inthe drawings. The thread-engaging disks 93 may be retained as theyprovide an effective guide for the thread in conjunction with the checkspring 91.

As shown in FIG. 2, from the check spring 91, the needle thread Nt isdirected to the needle 29 in a conventional manner, first to the wireguide 49, then to one thread-engaging loop 95 of a double-thread guide96 secured to the sewing head 14 beneath the takeup lever 30, then tothe takeup lever eyelet 32, next to another thread-engaging loop 97 ofthe double-thread guide 96, through a wire guide 98 on the needle barbushing 28 and to the needle.

The needle thread controlling mechanism of this invention, which isapplied to a sewing machine in addition to the conventionalthread-controlling means described above, is carried on a support plate100. As shown in FIGS. 1 and 2, a guard 101 for the takeup lever 30 issecured to the sewing head 14 by fastening screws 102. The guard 101 hasan arched rib 103 located outwardly on the path of the takeup lever anda flat base 104. The support plate may be fastened to the sewing head bythe same screws 102 which secure the guard 101 in place. Additionally,the guard 101 is preferably spaced slightly outwardly of the supportplate 100 by spacing a washer 105 at the top and by the double-threadguide 96 at the bottom and the base 104 of the guard 101 is transverselyslotted as at 107 so that thread may be directed into the space betweenthe base 104 of the guard 101 and the support plate 100. The base 104must, in addition, be formed with a vertical slot 108 overlying thetakeup accommodating slot in the sewing head. Moreover, the supportplate must also be formed with a vertical slot which is in alignmentwith the vertical slot 108 and through which the takeup lever 30extends.

On the upper portion of the support plate 100 above and to the left ofthe takeup lever 30, as viewed in FIG. 2, an auxiliary thread-tensioningdevice 110 is carried. The tensioning device 110 is termed auxiliarybecause in this invention the device 110 replaces the conventionaltension device 90 as the agency giving rise to tension control in theneedle thread.

The tension device 110 may be of any type known per se and preferablycomprises a transversely slotted and threaded stud 111 on which a pairof thread-engaging disks 112 are arranged. A beehive spring 113 iscarried on the stud between a washer 114 against the disks 112 and anadjusting nut 115 for regulating the spring pressure applied to thedisks 112. The flexible cable 56 is directed preferably to the washer114 of the thread-tensioning device for removing the pressure of thespring 113 from the disks whenever the presser foot is lifted.

A tab struck out from the supporting plate 100 is apertured to serve asa thread guide leading thread from a supply source (not shown) to thetensioning device 100. A wire thread guide 121 secured by a screw 122 onthe supporting plate 100 beneath the tensioning device directs thethread from the tensioning device.

Mounted behind the supporting plate 100 on the right-hand side of thetakeup lever on a fulcrum screw 123 is a bell crank 124 having one arm125 formed with a thread-guiding loop 126 which projects through a slot127 in the supporting plate 100. The other arm 128 of the bell crankextends upwardly beyond the top of the support plate and provides afinger grip 129 for adjustment of the position of the bell crank.Cooperating indicia 130 on the finger grip and on the support plate 100provide visual indication of the operator influenced setting of the bellcrank. A friction washer 131 on the function screw 23 or any other knownarrangement may be provided for deterring accidental movement of thebell crank 124.

Carried on the supporting plate 100 above the slot 127 is a deviceindicated generally at which acts as a one-way thread-clutching devicepermitting passage therethrough of the needle thread only in onedirection; i.e., toward the needle. The device 140 comprises a bracket141 secured by screws 142 to the supporting plate 100 and formed with anout and upturned ear 143 for supporting a fulcrum pin 144 for a lever145 fonned with thread-guiding notches 146, one at each end. The bracket141 beneath each extremity of the lever 145 is formed with a tab 147,which tabs may be notched to guide the thread to and from the lever 145and which additionally provide stops limiting pivotal movement of thelever.

Above the lever on the right-hand side of the fulcrum pin a 144 asviewed in FIGS. 2 and 4 is an abutment dog 150. The

dog is vertically slotted as at 151 to accommodate a clamp screw 152 bywhich the dog may be secured in selected position on the bracket 141.Two fingers 153 and 154 struck out from the supporting plate 100 embracethe abutment dog 150 so that together with the clamp screw 152 theabutment dog can be adjusted only in a vertical direction. A horizontalslot 155 in the abutment dog 150 accommodates an eccentric head portion156 of an adjusting crank 157. As shown in FIG. 4, a concentric stud 158on the adjusting crank is journaled in an aperture 159 in the supportingplate 100. When the clamp screw 152 is loosened, turning of theadjusting crank 157 will, therefore, result in fine adjustment of thevertical position of the abutment dog so that the sensitivity of theone-way threadclutching device may be regulated. A very light spring 160is preferably arranged between a tab 147 and the lever 145 to bias thelever toward the abutment dog 150.

The specific manner of threading a sewing machine equipped with thisinvention and the mode of operation is best illustrated abutment dogFIGS. 3 to 6. The needle thread N: is passed from a source of supply(not shown) to the auxiliary tensioning device 110, to thewire guide 121thence under the path of oscillation of the takeup arm 30 to thethread-guiding loop 126 of the adjustable bell crank 124. The threadthen is directed across the lever 145 of the thread-clutching device 140between the lever 145 and the abutment dog 150 thereof and thendownwardly to the check spring 91. As previously described, the threadis then directed through the pair of thread-guiding loops 95 and 97 ofthe guide 96 and between the thread-guiding loops to the takeup eyelet32, and thence to the needle.

In the sequence shown in FIGS. 3, 4, 5 and 6, the takeup lever 30 isshown respectively on the downstroke, at the very bottom of thedownstroke, in the identical position as in FIG. 3 but on the upstroke,and at the very top of the upstroke. In FIG. 3 the takeup arm is shownin a position on the verge of engaging the limb of needle thread betweenthe guides 121 and 126. For comparison of the influence of the parts onthe thread, three points along the thread are marked on FIGS. 3 to 6;point A being on the thread leading to the auxiliary tensioning device110; point B being initially along the thread leading to thethread-clutching device 140; and, point C being initially along thethread leading to the check spring 91.

As shown in FIG. 4, when the takeup lever 30 engages the thread betweenthe guides I21 and 126, the pull on the thread will cause thethread-clutching device 140 to nip the thread preventing any retrogrademovement of the thread, and consequently a measured amount of threadwill be drawn through the auxiliary thread-tensioning device 110 asindicated by the changed position of the point A on the thread.

As the takeup lever 30 begins to rise, as shown in FIG. 5, itsacceleration will be at a maximum so that the thread-clutching devicewill immediately be opened and that increment of the thread meteredthrough the auxiliary-tensioning device 110 will be drawn through thethread-clutching device and toward the check spring 91 as shown in FIG.5 by the changed positions of the points B and C along the thread.

By adjustment of the position of the bell crank 124 the amount of threadmetered into the system may be regulated. This amount of thread meteredinto the system may be varied from that amount required to set a tightstitch resembling that which is produced by a conventional sewingmachine, to an amount several times greater than required for a tightstitch so that a stitch with many times the minimum quantity of threadmay be formed.

As the takeup lever 30 rises to the top of the upstroke in FIG. 6, thelockstitch will be set or drawn into the work, and the unchangedposition of point A as compared with FIG. 5 illustrates that noadditional thread will be drawn into the system from the source ofthread supply. The needle thread moreover will with this invention neverbe drawn into the system in an uncontrolled manner such as might resultin the formation of uncontrolled thread loops on the fabric beingstitched. The amount of looseness of the stitching may be accuratelyadjusted so as to match precisely the shrinkages which will be inducedinto the threads and fabrics by sub sequent treatments so that a finalflat and pucker-free seam can be attained in the finished garment.

FIGS. 9 and 10 illustrate a bobbin thread pulloff mechanism which whenused with the needle thread controlling device of this inventionprovides for an advantageous uniformity in the distribution of threadlooseness as between the needle and bobbin threads of a lockstitch seam.As shown in FIG. 10, the

feed dog 74 of the work-feeding mechanism is formed with a transverseslot in the underside which slot is preferably not perfectlyperpendicular to the direction of work-feeding movement of the feed dogbut slightly canted relatively to the perpendicular. A thread-engagingwire 190 is fastened in the slot 180 so as to be positioned rearwardlyof the needle aperture 72 in the throat plate 71. FIG. 9 illustrates theloop taker 70 as the loop-seizing beak thereof has entered a needlethread loop N! and includes a representation of the bobbinthread-engaging wire at the forward position of the feed dog. The wire190 will, as shown in FIG. 9, loosen the bobbin thread Bt as it issuesfrom the loop taker and this looseness in the bobbin thread early ineach stitch-forming cycle eliminates resistance to passage of the needlethread loop Nt along the bobbin thread Br and upwardly into the workbeing stitched.

FIGS. 7 and 8 illustrate a modified form of construction of thisinvention, and moreover, illustrate alternative threading arrangementswhich are possible with this modified form.

The sewing machine illustrated in FIGS. 7 and 8 may be identical inconstruction and arrangement of conventional features to thatillustrated in FIGS. 1 and 2. The similarity to the construction of themachine of FIGS. 7 and 8 to that of FIGS. 1 and 2 also extends to theconventional needle thread handling means including the needle threadtensioning device 90, the check spring 91, the wire thread guide 49, thedoublethread guide 96 for leading thread to and from the eyelet 32 ofthe takeup lever 30. Like components of the sewing machine in themodification of FIGS. 7 and 8 have, therefore, been indicated by thesame reference characters as applied hereinabove to the construction ofFIGS. 1 and 2.

The needle thread controlling mechanism of this invention in the formshown in FIGS. 7 and 8 is carried on a support plate 200 which is formedwith a protrusion 201 snugly accommodating a boss (not shown) on thesewing machine so that the support plate may be securely fastened on thesewing machine by a single-fastening screw 202 threaded into the boss.The support plate 200 is preferably L" shaped and arranged to extendclosely adjacent to the path of oscillation of the takeup lever 30. Anauxiliary thread tension device 210 is carried by the support plate 200on the left-hand side of the path of the takeup lever 30 as viewed inFIGS. 7 and 3. The auxiliary tension device 210 may be identical to theauxiliary tension device 110 shown in FIGS. 1 through 6. A wire threadguide 212 is secured to the support plate 200 and accommodates severalturns of the thread from a source of supply (not shown) to the auxiliarytension device 210, so as to provide a slight pretension and to removekinks from the thread.

Fulcrumed on a screw 223 on the support plate 200 is a bell crank lever224 having one arm 225 formed with a threadguiding loop 226 arrangedclosely adjacent to the auxiliary thread tension device 210 andadjustable vertically relatively thereto upon turning of the bell cranklever 224. A second arm 228 of the bell crank protrudes beyond thesupport plate 201) and is formed with a finger grip 229. Indicia 230 onthe finger grip and on the support plate serve to delineate the positionin which the bell crank lever is set. A friction washer 231 on the screw223 deters accidental movement of the bell crank.

Indicated at 240 in FIGS. 7 and S is a thread-clutching device whichdiffers only in specific details of construction from thethread-clutching device 140 of FIGS. 1 through 6.

The thread-clutching device 240 includes a lever 245 notched at eachextremity to accommodate the needle thread and fulcrumed on a pin 244which is secured between the support plate 200 and an ear 243 struck outtherefrom. A thread camming projection 248 is struck out from thesupport plate 200 adjacent the upper extremity of the lever 245 tofacilitate insertion of a thread in the upper notched end of the lever245. A light coil spring 260 bears against the lever 245 and biases thelever against an abutment dog 250 secured by a screw 252 to the supportplate 200. A spring-adjusting bell crank 270 is fulcrumed on a screw 271on the support plate for regulating the pressure exerted on the lever245 by the coil spring 260.

In FIG. 7 which illustrates the threading of the device of thisinvention for the production of loose stitching, the principaldifferences of this modification from the form of construction shown inFIGS. 1 through 6 will be apparent. The needle thread Nt is directedfrom the auxiliary tensioning device 210 to the thread-guiding loop 226of the bell crank 224, and thence, directly to the lever 245 of thethread-clutching device. This limb of the needle thread N! passes overthe takeup lever 30 and intersects the path of motion thereof.Preferably, this limb of the thread additionally passes between thesupport plate 200 and a thread constraining finger 280 struck out fromthe side of the support plate 200.

The thread is then passed along the lever 245 and as in the previouslydescribed version, to the conventional thread-tensioning device 90 and,as described above, then to the takeup eyelet 32 and to the needle. Asin the previous version, the conventional thread-tensioning device 90 isnot used as a tension producing device so that its beehive spring may beremoved.

The angles which the thread makes approaching and leaving the lever 245differ markedly in the modification of FIG. 7 as compared with theversion shown in FIGS. 1 through 6. Assuming that uniform tension existsin the thread, the sharper angle of the thread approaching the leverwill result in a greater component of force being applied to the leverby the approaching thread than by the thread leaving the lever, and as aresult, the thread-clutching device will prevent retrograde movement ofthe thread more readily under such conditions when arranged as shown inFIG. 7.

In FIG. 7 the takeup lever 30 is shown substantially at the top ofstroke so that the limb of needle thread from the threadguiding loop 226to the thread-clutching device 240 will be distended by engagement withthe takeup lever 30, and the loop of needle thread passing through thetakeup eyelet 32 will also be distended. With this modification,therefore, the surplus thread for formation of loose stitches will bemetered into the thread-controlling system through the auxiliarytensioning device 210 during the same interval that the preceding stitchis being drawn up into the work. The thread-clutching device 240 will,however, separate these two functions. The thread drawn or meteredthrough the auxiliary tension device 210 on one upstroke of the takeuplever, will be available in the thread-controlling system for theformation of a loose stitch on the next succeeding upstroke of thetakeup. In fact, the check spring 91 which is fully distended in thestitchsetting position illustrated in FIG. 7, will return as soon as thetakeup lever 30 begins to descend and in returning the check spring 91will draw the freshly metered slack thread through the thread-clutchingdevice 240. Since the freshly metered thread will be available to thetakeup lever and to the needle early during the needle downstroke, loosethread will be available to facilitate needle penetration. The slackwhich is metered into the system during the stitch-setting portion ofeach cycle will remain available during the entire cycle so astoinfluence the formation of the succeeding stitch with surplus threadtherein in the same manner as previously described with respect to theform of construction illustrated in FIGS. 1 to 6. The amount of slackthread metered into the system at each stitch can be regulated bychanging the position of the bell crank 224 by shifting the finger grip229 thereof.

FIG. 8 illustrates the identical mechanism of FIG. 7 but with the needledirected differently. The threading shown in FIG. 8 will result inneedle thread handling generally in the conventional fashion, i.e., withthe stitches being set with ordinary tightness into the work, but withthe novel feature that the amount of thread in the needle threadhandling system may be changed at will so that this construction may beapplied to sewing machines having a wide range of different workthickness capacities, widely different needle bar strokes, etc.

In FIG. 8, from the thread-guiding loop 226, the needle thread isdirected over the takeup lever 30 over the threadguiding finger 280 andthen directly to the conventional thread-tensioning device 90, which asin previously described embodiments, has its thread-tensioning springremoved or rendered ineffective. The thread is then directed, asdescribed above, to the action of the check spring 91, the takeupeyelet, and to the needle. The thread-clutching device 240 iscircumvented in the arrangement of FIG. 8 so that at each upstroke ofthe takeup, the thread is subjected twice inseriatim to the influence ofthe takeup. By adjusting the position of the bell crank lever 224, theeffect of the takeup lever on the first limb of thread directedthereover may be regulated thus to vary the total takeup action on thethread.

Having set forth the nature of this invention, what is claimed hereinis:

1. A lockstitch sewing machine having an endwise reciprocatory threadcarrying needle, mechanism including a loop taker cooperating with saidneedle in the formation of lockstitches, and a needle thread takeupmeans partaking of recurring motion in timed relation with reciprocationof said needle, and means cooperating with said takeup member formanipulating a needle thread in the production of lockstitches havingcontrolled surplus slack thread therein, said means comprising athread-tensioning device for resisting passage of a thread from a sourceof supply to said needle, thread-guiding means for directing twosuccessive lengths of said thread extending between saidthread-tensioning device and said needle to the influence of said threadtakeup means, and a nipper acting on said thread between said twosuccessive lengths thereof and effective to prevent retrograde movementof said thread from said length entering to said needle to said lengthextending to said thread-tensioning device.

2. A lockstitch sewing machine as set forth in claim 1 in which saidthread-guiding means leads a first length of said thread extending fromsaid thread-tensioning device to said nipper across said path ofrecurring motion of said takeup means for influence by said takeup meansduring only a portion of each recurring motion thereof, and in whichsaid second length of said thread extending from said nipper to saidneedle is directed so as to provide for continuous influence by saidtakeup means.

3. A lockstitch sewing machine as set forth in claim 2 in which asupport is provided shiftably sustaining said threadguiding means fordirecting said first length of thread relatively to said recurring pathof motion of said takeup means, and an operator influenced regulator forshifting said thread-guiding means support to vary the portion of saidtakeup means recurring motion during which said first length of threadis influenced thereby.

4. A lockstitch sewing machine as set forth in claim 1 in which saidtakeup means includes a reciprocating takeup lever formed with a threadeyelet, in which said thread-guiding means leads a first length of saidthread extending from said thread-tensioning device to said nipperacross the path of reciprocation of said takeup lever remote from saidthread eyelet, and in which said thread-guiding means leads to a secondlength of said thread extending from said nipper to said needle throughsaid thread eyelet.

5. A lockstitch sewing machine as set forth in claim 4 in which saidpath of motion of said takeup means provides for an alternate drawing inand paying out of a thread loop of said second length of thread by saidthread eyelet, and in which said thread-guiding means positions saidfirst length of thread across that portion of said path of reciprocationof said takeup lever as to cause a drawing in of said first length ofthread by said takeup lever while said second length of thread is beingpaid out by said thread eyelet.

6. A lockstitch sewing machine as set forth in claim 4 in which saidpath of motion of said takeup means provides for an alternate drawing inand paying out of a thread loop of said second length of thread by saidthread eyelet, and in which said thread-guiding mean positions saidfirst length of thread across that portion of said path of reciprocationof said takeup lever as to cause a drawing in of said first length ofthread by said takeup lever while said second length of thread is beingdrawn in by said thread guide.

7. A lockstitch sewing machine as set forth in claim 1 in which saidnipper comprises a lever formed with a thread guide notch adjacent eachextremity for directing said thread along one side of said lever, afulcrum for said lever between said extremities, and abutment meansfixed relatively to said lever and located adjacent to that side oflever along which said thread is directed by said thread guide notchesfor engagement with said thread between said fulcrum and a thread guidenotch at one extremity of said lever.

8. A lockstitch sewing machine as set forth in claim 1 in which a checkspring is arranged to influence that one of said two successive lengthsof said thread directed by said threadguiding means which extends tosaid needle.

9. A lockstitch sewing machine as set forth in claim 1 in which a threadcarrying bobbin is arranged in said loop taker and in which a bobbinthread pulloff device is provided for slackening a thread carried bysaid bobbin during each reciprocation of said needle.

10. A lockstitch sewing machine as set forth in claim 9 in which saidmechanism cooperating with said needle in the formation of stitchesincludes a work feeding dog reciprocated alternately into and out ofengagement with a work fabric being stitched and in which said bobbinthread pulloff device comprises a bobbin thread engaging element securedon said work feeding dog and positioned so as to engage and slacken saidbobbin thread during each reciprocation of said work feed dog intoengagement with a work fabric.

Ill. A thread-controlling device for a lockstitch sewing machine havingan endwise reciprocatory needle, a needle thread takeup lever oscillatedin timed relation with said reciprocatory needle, a conventionalthread-tensioning device with a check spring and thread guide means fordirecting a thread from said check spring by way of takeup lever to saidneedle, said thread-controlling device including an attachment to saidconventional sewing machine arrangement comprising a support plateattachable to said sewing machine adjacent to said takeup lever, anauxiliary thread-tensioning device carried by said support plate, athread nipping device carried by said support plate and having a threadinlet, a thread outlet, and means for permitting movement of a threadtherethrough in only a direction from. said thread inlet to said threadoutlet, thread guide means carried on said support plate for directing athread between said auxiliary thread-tensioning device and said threadnipping device inlet, and means for securing said supporting plate on asewing machine with the thread outlet of said thread nipping devicelocated on the same side of the path of oscillation of said takeup leveras said conventional thread-tensioning device and with said thread guidemeans arranged to direct thread extending from said auxiliarythread-tensioning device across the path of oscillation of said sewingmachine takeup lever and to said thread nipping device.

1. A lockstitch sewing machine having an endwise reciprocatory threadcarrying needle, mechanism including a loop taker cooperating with saidneedle in the formation of lockstitches, and a needle thread takeupmeans partaking of recurring motion in timed relation with reciprocationof said needle, and means cooperating with said takeup member formanipulating a needle thread in the production of lockstitches havingcontrolled surplus slack thread therein, said means comprising athreadtensioning device for resisting passage of a thread from a sourceof supply to said needle, thread-guiding means for directing twosuccessive lengths of said thread extending between saidthreadtensioning device and said needle to the influence of said threadtakeup means, and a nipper acting on said thread between said twosuccessive lengths thereof and effective to prevent retrograde movementof said thread from said length entering to said needle to said lengthextending to said thread-tensioning device.
 2. A lockstitch sewingmachine as set forth in claim 1 in which said thread-guiding means leadsa first length of said thread extending from said thread-tensioningdevice to said nipper across said path of recurring motion of saidtakeup means for influence by said takeup means during only a portion ofeach recurring motion thereof, and in which said second length of saidthread extending from said nipper to said needle is directed so as toprovide for continuous influence by said takeup means.
 3. A lockstitchsewing machine as set forth in claim 2 in which a support is providedshiftably sustaining said thread-guiding means for directing said firstlength of thread relatively to said recurring path of motion of saidtakeup means, and an operator influenced regulator for shifting saidthread-guiding means support to vary the portion of said takeup meansrecurring motion during which said first length of thread is influencedthereby.
 4. A lockstitch sewing machine as set forth in claim 1 in whichsaid takeup means includes a reciprocating takeup lever formed with athread eyelet, in which said thread-guiding means leads a first lengthof said thread extending from said thread-tensioning device to saidnipper across the path of reciprocation of said takeup lever remote fromsaid thread eyelet, and in which said thread-guiding means leads to asecond length of said thread extending from said nipper to said needlethrough said thread eyelet.
 5. A lockstitch sewing machine as set forthin claim 4 in which said path of motion of said takeup means providesfor an alternate drawing in and paying out of a thread loop of saidsecond length of thread by said thread eyelet, and in which saidthread-guiding means positions said first length of thread across thatportion of said path of reciprocation of said takeup lever as to cause adrawing in of said first length of thread by said takeup lever whilesaid second length of thread is being paid out by said thread eyelet. 6.A lockstitch sewing machine as set forth in claim 4 in which said pathof motion of said takeup means provides for an alternate drawing in andpaying out of a thread loop of said second length of thread by saidthread eyelet, and in which said thread-guiding mean positions saidfirst length of thread across that portion of said path of reciprocationof said takeup lever as to cause a drawing in of said first length ofthread by said takeup lever while said second length of thread is beingdrawn in by said thread guide.
 7. A lockstitch sewing machine as setforth in claim 1 in which said nipper comprises a lever formed with athread guide notch adjacent each extremity for directing said threadalong one side of said lever, a fulcrum for said lever between saidextremities, and abutment means fixed relatively to said lever andlocated adjacent to that side of lever along which said thread isdirected by said thread guide notches for engagement with said threadbetween said fulcrum and a thread guide notch at one extremity of saidlever.
 8. A lockstitch sewing machine as set forth in claim 1 in which acheck spring is arranged to influence that one of said two successivelengths of said thread directed by said thread-guiding means whichextends to said needle.
 9. A lockstitch sewing machine as set forth inclaim 1 in which a thread carrying bobbin is arranged in said loop takerand in which a bobbin thread pulloff device is provided for slackening athread carried by said bobbin during each reciprocation of said needle.10. A lockstitch sewing machine as set forth in claim 9 in which saidmechanism cooperating with said needle in the formation of stitchesincludes a work feeding dog reciprocated alternately into and out oFengagement with a work fabric being stitched and in which said bobbinthread pulloff device comprises a bobbin thread engaging element securedon said work feeding dog and positioned so as to engage and slacken saidbobbin thread during each reciprocation of said work feed dog intoengagement with a work fabric.
 11. A thread-controlling device for alockstitch sewing machine having an endwise reciprocatory needle, aneedle thread takeup lever oscillated in timed relation with saidreciprocatory needle, a conventional thread-tensioning device with acheck spring and thread guide means for directing a thread from saidcheck spring by way of takeup lever to said needle, saidthread-controlling device including an attachment to said conventionalsewing machine arrangement comprising a support plate attachable to saidsewing machine adjacent to said takeup lever, an auxiliarythread-tensioning device carried by said support plate, a thread nippingdevice carried by said support plate and having a thread inlet, a threadoutlet, and means for permitting movement of a thread therethrough inonly a direction from said thread inlet to said thread outlet, threadguide means carried on said support plate for directing a thread betweensaid auxiliary thread-tensioning device and said thread nipping deviceinlet, and means for securing said supporting plate on a sewing machinewith the thread outlet of said thread nipping device located on the sameside of the path of oscillation of said takeup lever as saidconventional thread-tensioning device and with said thread guide meansarranged to direct thread extending from said auxiliarythread-tensioning device across the path of oscillation of said sewingmachine takeup lever and to said thread nipping device.